The present invention relates to path length control apparatus (PLC) for optical devices and in particular to a co-fired piezoelectric transducer that can be used in a PLC for a ring laser gyroscope and method of making the same.
A ring laser gyroscope (RLG) is commonly used to measure the angular rotation of an object, such as an aircraft. Such a gyroscope has two counter-rotating laser light beams that move within a closed loop optical path or xe2x80x9cringxe2x80x9d with the aid of successive reflections from multiple mirrors. The closed path is defined by an optical cavity that is interior to a gyroscope frame or xe2x80x9cblock.xe2x80x9d In one type of RLG, the block includes planar top and bottom surfaces that are bordered by six planar sides that form a hexagon-shaped perimeter. Three planar non-adjacent sides of the block form the mirror mounting surfaces for three mirrors at the comers of the optical path, which is triangular in shape.
Operationally, upon rotation of the RLG about its input axis (which is perpendicular to and at the center of the planar top and bottom surfaces of the block), the effective path length of each counter-rotating laser light beam changes and a frequency differential is produced between the beams that is nominally proportional to angular rotation. This differential is then optically detected and measured by signal processing electronics to determine the angular rotation of the vehicle. To maximize the signal out of the RLG, the path length of the counter-rotating laser light beams within the cavity must be adjusted. Thus, RLGs typically include a path length control apparatus (PLC), the purpose of which is to control the path length for the counter-rotating laser light beams for maximum signal.
One such known PLC 10 for a block 12 of a RLG 14 is illustrated in FIGS. 1-2. The PLC 10 includes a piezoelectric transducer (PZT) 16 which is secured to a mirror 18 via an epoxy-based adhesive 20. The epoxy adhesive 20 completely covers the interface (defined by a lower surface 22 of the PZT 16 and an upper surface 24 of the mirror 18) between the PZT 16 and the mirror 18. The mirror 18 is secured to a mirror mounting surface 26 of the optical block 12. The mirror 18 communicates with laser bores 32 (only partially shown) of an optical cavity 34 (only partially shown) of the block 12. The bores 32 partially form a portion of the closed loop optical path 38 defined by the optical cavity 34. As seen in FIG. 1, the mirror 18 reflects counter-rotating laser light beams 40 at its respective corner of the closed loop optical path 38.
Conventional PZT 16 (perhaps shown best in FIG. 2) is defined by a pair of piezoelectric elements 42 and 44. A conductive tab 45 is sandwiched between the elements 42 and 44, which are bonded to the conductive tab 45 by thin layers of conductive epoxy. Opposite polarity conductive tabs 41 and 43 are adhered to the outer major surfaces of elements 42 and 44, respectively, also by thin layers of conductive epoxy. The opposite polarity leads 47 and 49 extend from the positive conductive tabs 41 and 43, respectively. Another lead 48 extends from the negative conductive tab 45. As shown in FIG. 1, the opposite polarity leads 47 and 49 are electrically connected to form a single lead 46, and the leads 46 and 48 extend from the PZT 16 and are connected to terminals 50 and 52 of a wireboard element 54. Leads 58 and 59 extend from the terminals 50 and 52, respectively, of the wireboard element 54 and are coupled to a regulated voltage source (not shown) which is in turn coupled to a detector (not shown) which monitors the intensity of the light beams 40. The PZT 16 takes an applied voltage delivered by the regulated voltage source, in response to a signal provided by the detector, and turns this voltage into small but precisely controlled mechanical movement. This mechanical movement of the PZT 16 affects translational movement (as represented by double-headed arrow 60) of the mirror 18, and thereby controls the laser light beam path length.
The present invention is a multi-layer PZT fabricated as a multi-layer ceramic assembly. The multi-layer PZT of the present invention has contacts, which are electrically connected to other layers within the multi-layer PZT, formed directly on the top layer of the PZT, and the regulated voltage source can be coupled directly to the PZT at the top layer contacts. The present invention is a multi-layer piezoelectric transducer that can be used as a path length control apparatus of an optical device. The multi-layer piezoelectric transducer includes a plurality of ceramic layers so as to form a stack, wherein each ceramic layer has first and second opposing surfaces. The plurality of ceramic layers includes a top layer at a first end of the stack having a top conductive pattern formed on the first surface thereof. The top conductive pattern includes a negative contact and a positive contact. The plurality of ceramic layers also includes at least one poled ceramic layer having a conductive pattern formed on the first surface thereof. The plurality of ceramic layers include additional poled ceramic layers having alternating conductive patterns formed on the first surface thereof.